The invention relates to an apparatus for directing and steering the foremost part of a drillstring for earth drillings.
Such an apparatus is known.
When, by an embodiment of the known apparatus, one has to drill further to create a side branch starting from a vertical bore, the drillstring is first retrieved from the borehole, a wedge shaped guiding piece is next let down into the borehole, and subsequently the drillstring is again lowered in the borehole. The wedge shaped guiding piece deviates the foremost part of the drillstring sidewards, so that the borehole is drilled in a more horizontal direction, to form the required side track.
With another embodiment of the known apparatus for the forming of a side branch starting from the vertical bore, the bottom end of the drillstring includes a bend piece which carries the bit and a drilling motor. To form the side branch, the bit is driven by the drilling motor and non rotating drillstring, and consequently is drilled ahead sidewards to form the required side track.
Another embodiment of the known apparatus for yielding a sideward deviation from the vertical borehole comprises one or more stabilizers for deviating the foremost part of the drillstring.
All these embodiments of the known apparatus require, for the incorporation of the wedge shape guiding piece, or of the bend piece at the bottom end of the drillstring, or of the stabilizers, that the whole drillstring be retrieved from the borehole, and to subsequently lower down the tapered shaped guiding piece in the borehole, or to incorporate the bend piece or the stabilizers at or nearby the bottom end of the drillstring.
This repetitive retrieving of the drillstring out of the borehole, to make the necessary arrangements for further sidewards drilling starting from the vertical borehole, is very time consuming and costly.
The invention intends to eliminate these disadvantages of the known apparatus or apparatuses.